I have an internet coaxial cable that used to be screwed into the back of a cable box for cable TV.
I have eliminated my Cable TV subscription, but I still have internet service.
I have purchased a Roku Ultra device with an Ethernet port.
I wish to set up a wired internet connection to the Roku device.
How can I adapt the internet coaxial cable to plug into the Ethernet port
of my Roku Ultra device?
Most cable providers use what is called DOCSIS as the protocol to provide both Internet and TV over a coaxal cable. You must have a device that takes the data from the coax and converts it and sends it out over Ethernet and/or WiFi.
But you can't buy just any old cable modem you find at your local Best Buy or some web site. You need to ensure it's compatible with the service your cable company offers. There's different versions of DOCSIS, so you need to ask your cable provider what is needed for the service you are paying for.
Next, most modems will include a router in the same box, which is necessary for your personal network security. It would also provide multiple Ethernet jacks to connect additional devices, and likely will also include a WiFi access point.
When you check with your cable provider, you might find that you can rent a modem from them. Depending on what they offer, it might actually be a better deal to rent a box instead of buying your own. For example, I have Comcast/Xfinity Internet service, along with a voice line. While I pay them $20 per month to rent the box, it also gives me unlimited data on my Internet plan. If I paid for unlimited data, it would cost me more per month than renting the modem. So in the end it's less expensive to rent a modem, and I didn't have to pay $150 to buy one.
The "adapter" you need is a cable modem compatible with and configured to connect to your internet service.
Internet coax --> Cable modem --> Ethernet cable --> Roku
